1. Field of the Invention
The present invention relates generally to a mobile communication system for high-speed packet transmission, and in particular, to an apparatus and method for communicating control information needed for demodulation of a packet data transmission channel.
2. Description of the Related Art
In general, a mobile communication system for high-speed packet transmission is divided into two systems, one system supporting only data transmission and another system supporting voice transmission as well as data transmission. The mobile communication system for high-speed packet transmission is designed to use a high-speed packet data transmission channel for a high-speed data service. The high-speed packet data transmission channel (e.g., a packet data channel (PDCH) of 1xEVDO and 1xEVDV) is shared by a plurality of users on a time division multiplexing (TDM) basis in order to transmit data at high speed.
In the mobile communication system for high-speed packet transmission, a transmitter transmits control information, to control the transmission of data. The data is transmitted through the high-speed packet data transmission channel on a TDM basis, over a packet data control channel (PDCCH), also known as a preamble channel. To provide a data service through the high-speed packet data transmission channel, a mobile terminal must receive control information for the data containing information pertaining to a destination, a data length, a data rate and a modulation mode, among others, of the data transmitted at a specific point in time.
The control information for the packet data includes subpacket length information, MAC (Medium Access Control) ID, data rate, modulation mode, payload size, subpacket ID (SPID), and ARQ (Automatic Repeat Request) channel ID. As mentioned above, in the mobile communication system for high-speed packet transmission, a transmission unit of the data transmitted through the high-speed packet data transmission channel is called a “subpacket”, and the “subpacket length information” refers to the time required to transmit the data over the high-speed packet data transmission channel on a TDM basis. A system supporting a variable data length must transmit this information to the mobile terminals. The MAC ID, an identifier for mobile terminal identification, is assigned to the mobile terminal desiring to receive a high-speed packet data service during system access. The “data rate” is a transfer rate of data having the subpacket length, and the “modulation mode” indicates a selected one of QPSK (Quadrature Phase Shi Keying), 8PSK (8-ary Phase Shift Keying), 16QAM (16-ary Quadrature Amplitude Modulation) and 64QAM (64-ary QAM) modulations used to modulate the transmission data. The “payload size” refers to the number of information bits constituting one subpacket, and the subpacket ID (SPID), an identifier of each of the subpackets, is used to support retransmission. The ARQ channel ID, an identifier for supporting continuous data transmission to one mobile terminal, is used in identifying a parallel transmission channel.
As described above, in the mobile communication system for high-speed packet transmission, the control information transmitted over the packet data control channel includes 2-bit subpacket length information, 16-bit MAC ID, 2-bit payload size, 2-bit SPID and 2-bit ARQ channel ID, and the data rate and the modulation mode are determined depending on the 2-bit subpacket, the 2-bit payload size and Walsh function information used for packet data transmitted over a packet data transmission channel transmitted through another channel. Thus, upon receiving packet data after being assigned MAC ID during system access, a mobile terminal (or user) desiring to be provided with the high-speed packet data service demodulates the received packet data control channel and analyzes the MAC ID to determine whether the received packet is destined thereto. If so, the terminal demodulates the packet data using information on subpacket length, payload size, SPID and ARQ channel ID, acquired by demodulating the packet data and information on a Walsh function used for packet data channel transmission. Here, information on a data rate and a modulation mode of the received subpacket is determined based on a combination of the subpacket length, the payload size and the Walsh function used for the packet data channel.
For example, the mobile communication system for high-speed packet transmission transmits the packet data control information using two packet data control channels: a forward primary packet data control channel (PPDCCH) and a forward secondary packet data control channel (SPDCCH). Such packet data control channels are utilized along with the packet data channel (PDCH) on a code division multiplexing (CDM) basis. That is, the forward primary packet data control channel, the forward secondary packet data control channel and the packet data channel are assigned different code channels, and the channels are all transmitted on at the same time.
As descried above, since the packet data channel and the packet data control channels are simultaneously transmitted upon, it is very important for a receiver to promptly demodulate data on the two packet data control channels without error. Accordingly, there is a demand for a scheme capable of efficiently transmitting various control information for demodulation of data on the packet data channel.